*The legions and auxilia.* The legionaries were recruited from Roman citizens or from provincials who received Roman citizenship upon their enlistment. Their units of organization, the legions, comprised nearly 6000 men, of whom 120 were cavalry and the rest infantry. The number of legions was at first eighteen, but was later raised to twenty-five, giving a total of about 150,000 men. The auxiliaries, who took the place of the contingents of Italian allies of earlier days, were recruited from among the most warlike subject peoples of the empire and their numbers were approximately equal to the legionaries. They were organized in small infantry and cavalry corps (cohorts and _alae_), each 480 or 960 strong. At the expiration of their term of service the auxiliaries were granted the reward of Roman citizenship. *The praetorians.* A third category of troops, which, although greatly inferior in number to the legions and auxiliaries, played an exceptionally influential rôle in the history of the principate, was the praetorian guard. This was the imperial bodyguard which attended Augustus in his capacity of commander-in-chief of the Roman armies. It owed its influence to the fact that it was stationed in the vicinity of Rome while the other troops were stationed in the provinces. Under Augustus the praetorian guard comprised nine cohorts, each 1000 strong, under the command of two praetorian prefects of equestrian rank. The praetorians were recruited exclusively from the Italian peninsula, and enjoyed a shorter term of service and higher pay than the other corps. *Conditions of service.* It was not until 6 A. D. that the term of enlistment and the conditions of discharge were definitely fixed. From that date service in the praetorian guard was for sixteen years, in the legions for twenty and in the _auxilia_ for twenty-five. At their discharge the praetorians received a bonus of 5000 denarii ($1000), while the legionaries were given 3000 denarii ($600) in addition to an assignment of land. The discharged legionaries were regularly settled in colonies throughout the provinces. To meet this increased expense Augustus was obliged to establish a military treasury (the _aerarium militare_), endowed out of his private patrimony, and supported by the revenue derived from two newly imposed taxes, a five per cent inheritance tax (_vincesima hereditatium_) which affected all Roman citizens, and a one per cent tax on all goods publicly sold (_centesima rerum venalium_). *The fleets.* For the policing of the coast of Italy and the adjacent seas Augustus created a permanent fleet with stations at Ravenna and Misenum. Conforming to the comparative unimportance of the Roman naval, in contrast to their military establishment, the personnel of this fleet was recruited in large measure from imperial freedmen and slaves. Only after Augustus were these squadrons and other similar ones in the provinces placed under equestrian prefects.